Surface-Molecule Interaction Strength on CO₂ Adsorption Capacity in Nanopores: Implications to Advance CO₂ Sequestration Performance

CO2 geological sequestration, injecting CO2 into tight salt caverns or depleted oil/gas reservoirs where a diversity of nanopores exists, is recognized as a reliable and applicable approach to achieve efficient CO2 reduction. The adsorption mechanism induced by the surface-molecule interaction is the underlying reason why nanopores have an obvious stronger CO2 storage capacity than macropores. However, the magnitude that the CO2 storage performance would be improved by intensifying the surface-molecule interaction strength is still a giant knowledge gap. A clear understanding of the relationship between surface-molecule interaction strength and the nanoconfined CO2 adsorption capacity provides critical guidance on modifying surface composition aiming at better CO2 sequestration performance. In this work, the simplified local density (SLD) theory in accordance with the equilibrium of chemical potential lays the fundamental basis, and the shift of CO2 critical properties as the surface-molecule interaction strength varies is taken into account. Results indicate the following: (a) Manipulating surface-molecule interaction strength imposes a significant impact on CO2 adsorption phase density in nanopores; the CO2 storage amount in a 2 nm pore would improve by as much as 103%, while the interaction strength enhances from 100 to 500 K; (b) The discrepancy in terms of nanoconfined average CO2 density due to changing interaction strength is fairly evident at low-pressure conditions but greatly mitigated under high-pressure conditions where the bulk CO2 density approaches the adsorption phase density; (c) Neglecting the shift of CO2 critical properties in nanopores leads to the overestimation in nanoconfined average CO2 density, and a magnitude that could exceed 30% has a positive correlation with the rise of surface-molecule interaction strength as well as the decline in pore size. This work explores the key dependence of the nanoconfined CO2 storage on surface-molecule interaction and highlights the huge potential to advance CO2 sequestration efficiency by nanopore surface modification.